The invention relates to a device for driving a body that, in order to perform a tumbling and rotating movement that is based on the principle of the invertable link chain, is suspended by means of pivot pins on two fork-shaped gimbals so that it moves about two axes that are askew to one another, which gimbals are each connected by means of a pivot bearing to the end of one of two parallel drive shafts which, in order to achieve uniform movement of the body, must rotate in opposite directions and at alternately interchanging increasing and decreasing angular speeds..
A tumbling and rotating body of this type is used especially as a hollow body for receiving material to be treated, which material is to be subjected to physical or chemical processes, the simultaneous tumbling and rotating movement achieving particularly favourable effects with regard to the course of such processes.
The body tumbling and rotating in the described manner is used especially for mixing, and the movement, which in known manner is based on the principle of the invertable link chain, does not allow centrifugal forces to arise which produce a separating effect. The advantage of the tumbling and rotating movement lies in the fact that each point on the body describes a three-dimensional path with no nodal point.
When considering a drive means for a body that is suspended in the manner described for the purpose of performing a tumbling and rotating movement it should be taken into account that each of the shafts on which the body is pivotally mounted by means of gimbals must rotate non-uniformly if an even distribution of the accelerations and decelerations that are required alternately on both shafts is to be achieved in the course of movement. If this condition is not fulfilled, the body moves non-uniformly, with the result that the above-mentioned special effects on the material to be treated in the body cannot be achieved and that premature wear to important parts of the machine will occur, especially in the bearings.
The above-described drive problem, which lies in the fact that when the angular speed of one shaft increases the other shaft must rotate at a decreasing angular speed, which process must continuously and alternately apply to each of the two shafts, is due to the special course of movement of this inversion-kinematic system. This non-uniformity of the angular speeds of the shafts for driving the body, which is stipulated by the system, gives rise to the difficulties involved in solving the problem of the drive means. Various proposed solutions are known.
DE-PS No. 1 145 455 discloses a solution to this problem which provides a positive drive mechanism using a universal joint between the shaft that is connected to the fork-shaped gimbal and a motor-driven shaft that forms an angle of 45.degree. with the extended axis of the first shaft, which shaft is driven thereby. In the case of a universal joint, as is known, there occur periodically-changing angular speeds having a sinusoidal course. Apart from the large amount of space required by the entire drive means, the acute angle of 45.degree. is also unfavourable. Wear occurs too rapidly, and the universal joints, which transfer the entire torque, vibrate. This solution has not proved satisfactory in practice.
For solving the problem of the drive means using a non-positive drive mechanism, a device for producing a tumbling and rotating body movement disclosed in DE-PS No. 1 207 750 has a compensating gear in the form of a frictional ball-mechanism on one of the drive shafts. A ball-bearing cage is arranged between a driving ring, which is arranged loosely on the drive shaft and is driven uniformly by a drive element, and a driven ring that is also arranged loosely on the drive shaft, which cage is keyed onto the shaft and causes the drive shaft to rotate, whilst the driven ring, which turns in the opposite direction to the shaft, is rigidly connected to a chain wheel in order, by way of a chain, to turn the second drive shaft, which is arranged in parallel in the opposite direction. Since, however, the two drive shafts rotate non-uniformly (while one drive shaft decelerates the other accelerates), in this compensating gear so much friction must inevitably arise that this solution is unsuitable for prolonged operation. This solution has therefore also proved unsatisfactory in practice and could never be utilised commercially.
Since the proposed solutions described above have too many shortcomings when put into practice, in the search for a suitable drive means a so-called pendulum drive means, known from CH-PS No. 496 912, has been developed in which on the drive shaft there is arranged a pendulum which is pivotally connected thereto and on which there is arranged a control element which is positively coupled to the shaft and is preferably in the form of a crank that is rotatably mounted on the pendulum and, being in operative connection with at least one fixed point on the device, produces a periodic swinging movement of the pendulum in dependence upon the speed of the shaft. The crank is driven by the shaft by means of a belt at half the speed of the shaft. The fixed point on the device that is in operative connection with the control element in the form of a crank is a guide slot in which the crank pin slides back and forth. On each revolution of the drive shaft the pendulum performs two complete backward and forward movements, and when the pendulum moves in the same direction as the direction of rotation of the drive shaft, acceleration occurs as a result of the superimposition of the two movements, and when the pendulum moves in the opposite direction, deceleration occurs. The resulting course of movement does not exactly follow a sinusoidal line, however, so that in order to obtain an ideal solution it is necessary to make further structural improvements in order that at every moment during movement the guide slot for the crank is in a position parallel with the longitudinal axis of the pendulum.
This drive means, which is suitable for practical purposes, has, however, the disadvantage that it is possible to drive only one shaft connected by means of the fork-shaped gimbal to the body to be set in motion, whilst the second shaft, which is connected to the body by way of the other fork-shaped gimbal, as a result of this connection via the gimbals also turns at the non-uniform angular speed characteristic of this system. The use of this drive means considerably reduces manufacturing costs and the space requirement in comparison with the drive means mentioned above and disclosed in DE-PS No. 1 145 455, but since only one shaft is driven and it is possible to obtain only a good approximation to the course of the angular speed, which is sinusoidal in an ideal case, a drive means of this construction sets certain limitations with regard to the size and weight of the body to be set in motion.
In order therefore to drive two shafts which are each connected by means of a fork-shaped gimbal to the body to be set in motion, U.S. Pat. No. 4,341,475 proposes a solution which provides for each of the shafts a resilient shaft coupling between a uniformly driven shaft part and the shaft part that is connected to the fork-shaped gimbal, there being supported between the coupling parts, against each of the two coupling parts displaced by an angle of 180.degree., balls and compression springs as energy storage means which are arranged in a circle alternately one behind the other and which allow a periodically repeated relative rotation of the coupling parts with respect to one another and thus, when energy is being stored, allow a deceleration and, when the stored energy is being released, allow an acceleration of the coupling part that is fixed to rotate with the shaft, the other uniformly driven coupling part being arranged to rotate relative to the shaft. Although this solution is suitable for relatively small bodies that are to be set in a tumbling and rotating motion, it cannot, however, produce the body movement that is necessary to obtain optimum mixing results which can be achieved only by a positive drive means, since this solution is characterised by a greater or lesser degree of resilience in the driving elements. The accelerations and decelerations required alternately on the two shafts do not take place at the correct moment as a result of the resilient members that are incorporated into the drive system, so that the rhythm of movement is interfered with. As a result of the unrhythmic behaviour, an unnecessary loss of energy occurs and the shaft couplings are subject to increased load, which also gives rise to the disadvantage that the springs can become weak, and it can easily be imagined that if the springs on only one shaft coupling are weakened the entire rhythm will go out of control. It has been shown in practice that mixing machines using the body as a mixing container result in poorer mixing results than machines equipped with a positive drive means, such as, for example, the above-mentioned universal joints, but the latter machines have proved to have little suitability in industrial practice.